Various devices have been developed for sensing and measuring the concentrations of different gases at man-made or natural locations, such as oil wells, pipelines, mines, manufacturing plants, refineries, and the like. Monitoring for the presence and concentration of gases may be used for various applications, such as to ensure that toxic gases (CO, H2S, etc.) are not present in significant concentrations, to ensure that explosive gases (CH4, H2, etc.) are below respective explosive limits, to identify the gases in a mixture (for custody transfer, heat content, etc.), or for various other reasons. Spectroscopy may be used to provide highly sensitive and selective sensors because each gas exhibits a unique spectroscopic fingerprint, such that gases absorb and emit light energy at specific wavelengths. Gases are relatively transparent, however, so the absorption line strength of a gas may be relatively small and hard to detect.
To accommodate for the small absorption line strength, light used in spectroscopy is required to pass through long path lengths in the gas in order to establish sufficient sensitivity for a spectroscopic sensor to provide a measurement of a concentration of a gas of interest in a test sample, for example. For example, a light source of the spectroscopic sensor may be separated from a detector of the spectroscopic sensor by a distance of one kilometer or more to achieve a necessary path length, but such distances are not practical in most applications.
Other known types of spectroscopic sensors define an optical cavity with two mirrors and are referred to as optical cavity sensors. The gas is contained within the optical cavity, and the light is reflected between the two mirrors multiple times before being detected. While this technique allows for a manageable device size, it is problematic due to the need to maintain very exacting alignment of the mirrors. Variations in conditions, such as temperature changes, vibration, humidity, or the like, may misalign the mirrors or otherwise interfere with the sensitivity and/or accuracy of these optical cavity sensors. Therefore, this technique is generally not used for remote, unattended measurements in various field environments, such as an oil or gas well pad, a pipeline, a mine, or the like. Moreover, optical cavity sensors are generally quite expensive.
Some gas leak detection systems use a sensing pipe or tube located near a pipeline through which the gas is conveyed. This sensing pipe or tube may have openings to allow gas leaking from the pipeline to diffuse into the sensing pipe or tube. A burst of air or another gas may be introduced into the sensing pipe or tube to move the gas leaking from the pipeline through the sensing pipe or tube. The sensing pipe or tube may include a gas sensor at one end to sense the leaking gas that is pushed through the sensing pipe or tube by the air burst toward the sensor.
These types of leak detection systems may be unable to accurately determine the location of the leak along the length of a very long pipeline. The location of the leak is approximated based on the concentration of the gas detected at the sensor and the time delay between when the air burst is introduced into the sensing pipe or tube. Because the gas may disperse along the length of the sensing pipe or tube by the air burst, it can be difficult or impossible to accurately determine where the gas first diffused into the sensing pipe or tube if the gas must travel through the tube for a very long distance before reaching the sensor at the end of the tube.